Recovery of distillate hydrocarbons from well fluids



4 7441 BY (14AM. ATTORNEY 2 Sheets-Sheetl INVENTOR [27 S E. S. HILL Filed Aug. 51,

RECOVERY OF DISTILLATE HYDROCARBONS FROM WELL FLUIDS Aug. 17, 1943.

E. S. HILL Aug. 17, 1943.

RECOVERY OF DISTILLATE HYDROCARBONS FROM WELL FLUIDS ZSheets-Sheet 2 Filed Aug. 51, 1939 .INVENTOR lzzl ZS.7%Z& BY

ATTORNEY Patented Aug. 17, 1943 RECOVERY OF DISTILLATE HYDRO- CARBONS FROM WELL FLUIDS Earl S. Hill, Tulsa, kla., assignor to Stanolind Oil & Gas Company, Tulsa, Okla, a. corporation of Delaware Application August 31, 1939, Serial No. 292,818

7 Claims.

This invention relates to the recovery of distillate hydrocarbons from well fluids containing the same. More particularly it relates to improved processes for recovering such distillate hydrocarbons at high pressures whereby the residual gas can be injected into an underground reservoir with a minimum of compression.

Naturally-occurring reservoirs have been discovered in recent years in which both normally gaseous and normally liquid hydrocarbons exist, principally in a uniformly distributed condition usually referred to as a gas phase. In producing from such reservoirs it has been found that reducing the pressure of the well fluids causes the separation of a relatively small amount of a volatile liquid hydrocarbon fraction from the residual gas which can be recovered by means of a trap or separator. This liquid fraction is called distillate and the wells producing from such reservoirs are now classified as distillate wells.

The reservoirs from which distillates are produced are invariably at high pressures and temperatures, for example 2000 to 4000 or more pounds per square inch and 125 to 225 F. or higher, and the distillate well fluids almost always contain a great preponderance of the lighter hydrocarbons, the methane content thereof being generally above 80% and usually in the vicinity of 90% by volume. The content of butanes and heavier hydrocarbons is small and consequently these hydrocarbons are difficult to recover in satisfactory yields. 4

It is well understood that the condensation of dist llate upon reducing the pressure of the well fluid is due to the phenomenon known as retrograde condensation which occurs at relatively high pressures and between the critical temperature of the hydrocarbon mixture under consideration and the maximum dew point of that mixture. At each temperature within these limits there is a pressure at which the maximum yield of distillate can be separated from a well fluid containing the same and this maximum yield increases with decreasing temperature. The usual method of recovering distillate from such a well fluid is by reducing its pressure, for example by expansion through a valve with or without auxiliary cooling to a desired pressure, for example 700 to 1200 pounds per square inch and then separating the condensed liquid from the residual gas. Generally suflicient cooling is employed so that the separation is carried out at a temperature below +50 F., for example at 0 to +40 F.

The efiect of producing from distillate-containing reservoirs upon the material remainin therein is extremely important. If the reservoir pressure is allowed to decrease during production more and more of the valuable normally liquid hydrocarbons therein will be precipitated by virtue of the retrograde condensation phenomenon and thus will not be produced with the well fluid. It is therefore desirable to recycle the residual gas after the recovery of distillate therefrom to the producing formation in order to maintain its pressure and avoid loss of distillate as explained above. Recycling in this manner, however, involves the recompression of large volumes of residual gas to pressures in excess of well head pressures and the cost of such compression is very high, especially if the separation of distillate is carried out at a relatively low pressure.

From the above it will be understood that the customary method of distillate recovery with recycling has a considerable number of disadvantages among which are limited yield of distillate, high cooling costs and high compression costs. Another disadvantage incident to the use of low separator temperatures is the danger of natural gas hydrate formation in the apparatus due to the small amount of moisture present in substantially all distillate well fluids.

I have found that all of the above disadvantages can be substantially completely eliminated by changing the composition of the well fluid being processed by contacting the same with a relatively non-volatile liquid miscible with the distillate in an amount suflicient to increase the critical temperature of the resulting system to ordinary atmospheric temperature or above and separating the liquid material from the residual gas at a temperature below that critical temperature. Since the separation step according to my method is carried out on a mixture below its critical temperature the retrograde condensa tion phenomenon is not involved but the normal sequence of condensation and vaporization occurs. Also the temperature-pressure-yield relationship is changed in such a way that improved distillate yields are obtained at pressures much higher than can be economically used in processing the well fluid alone, thus greatly reducing the compression costs incident to recycling operation. Obviously separation at atmospheric temperature or above either eliminates the gas hydrate problem or allows the use of simple and inexpensive types of water removal.

In distillate recovery processes of the type last mentioned, I have found further that efliciency is increased and costs lowered by carrying out the contacting operation at a pressure above 1500 pounds per square inch and preferably at a pressure in the range from about 2000 to about 4000 pounds per square inch and heating the separated liquid fraction at substantially the same pressure to remove a portion of the normally gaseous constituents therefrom prior to reduction of pressure to produce the desired distillate hydrocarbons. The heating step gives in effect a partial stripping action which materially increases the proportion of fixed hydrocarbon gases released at high pressure for recompression rather than at a lower pressure which would, of course, require additional compressor capacity, Another feature of great practical importance is based upon the fact that most distillates containa small percentage of material boiling above the usual boiling range of gasoline. This relatively heavy material is particularly suitable for introduction into the contacting stage and its use in that manner eliminates the cost involved in providing an extraneous relatively non-volatile contacting medium. These and other features will be hereinafter described more fully.

It is an object of my invention to provide a novel and efficient process for recovering distillate hydrocarbons from well fluids containing the same. Another object is to provide an improved process for recovering increased yields of distillate while eliminating the residual gas from the system at high pressure whereby the cost of recycling the same to the producing formation is minimized. A further object is to provide a distillate recovery method which will economically separate and produce a high ratio of high pressure residual gas to low pressure gas. Further objects and advantages of my invention will be apparent from the following detailed descrintion thereof read in conjunction with the drawin s, in which:

Figure 1 represents in diagrammatic form a preferred distillate recovery plant according to my invention, and

Figure 2 represents a second form of apparatus a cording to my invention, also in diagrammatic form.

In one of its broad asnects my invention comprises contacting a distillate well fluid at a high pressure in excess of 1500 pounds per square inch with a relatively non-volatile liquid medium miscible with the distillate hydrocarbons, separating residual gas from the resulting liquid phase and heat ng the latter without substantial pressure reduction to drive off an additional quantity of undesirably light gases. in the contacting step is maintained in the range from about 2000 to about 4000 pounds per square inch, for example 2500 pounds per square inch, and the temperature in the range from about 75 F. to about 125 F., suitably about 100 F. While any convenient contacting method can be employed this operation is best carried out countercurrently in a bubble plate tower or the like and the heating step performedfln the lower portion thereof. In any case it is desirable that the gases evolved in the heating step be returned to the contacting zone to prevent undue loss of the butanes and heavier hydrocarbons present therein. The high pressure residual gas is preferably compressed for injection into the producing formation. Under some conditions it may be desirable to compress the well fluid prior to treatment in accordance with my invention and inject the residual gas directly into an input well Preferably the pressure and this can be done without departing from my invention.

As the relatively non-volatile liquid introduced into the contacting step I can use any liquid material less volatile than the distillateto be recovered and miscible therewith. This can be, for example, an absorption oil or gas oil from an extraneous source, but preferably is a heavy distillate fraction separated from the desirable portions thereof by fractionation. Thus when motor gasoline is being produced the relatively heavy fraction will have an initial boiling point in the neighborhood of 400 F. whereas the initial boiling point can be as low as 260 F.-300 F. when natural gasoline meeting market specifications is the desired product. In any case the relatively heavy oil is introduced into the contacting zone in sufilcient quantity to increase the critical temperature of the hydrocarbon system above the temperature at which the residual gas is withdrawn from the contacting step, but usually a somewhat greater amount, for example, about 2 to 6 gallons per thousand cubic feet are employed in order to obtain still greater yields.

As stated above a small quantity of water generally accompanies distillate well fluids and this is preferably removed in order to avoid emulsion difllculties in the contacting step and under some conditions to avoid natural gas hydrate formation. A simple and effective method of doing this is to introduce the well fluid at well head pressure with or without some preliminary cooling into a separator and remove the liquid water from the lower portion thereof. Generally speaking, a certain proportion of the distillate hydrocarbons'are in the liquid phase at the well head because of the pressure drop occurring in the tubing and this also collects in the water separator as an upper layer, which can be withdrawn from the system or introduced into the contacting zone or into a subsequent fractionating zone if desired.

Further details of my invention can best be understood from the description of the apparatus shown in the drawings and the manner in whic they operate in accordance therewith.

Referring now to Figure 1 a producing well I0 is shown which is of the distillate type as hereinbefpre defined. The well fluid flowing therefrom at the well head will be at a relatively high pressure and temperature, for example about 1500 to 4000 or more pounds per square inch and about 75 F. to 225 F. depending primarily upon the bottom hole temperature and pressure, the composition and the rate of production.- This fluid passes through valve II and line l2 and either through valve l3 or through valve l4, cooler l5 and valve IE to separator l1. Normally these valves are manipulated so that there is no substantial pressure reduction between the.

well ill and separator I1. In order to remove as much water from the well fluid as possible sumcient cooling is preferably supplied by cooler I5 liquid level control 2|. The material in line 29 can be either removed from the system through valve 22 and line 23 or introduced into other parts thereof through line 24 as will be described below.

The well fluid, which now has a substantially reduced water content, is removed from the upper portion of separator l1 and passes by means of line 25 through pressure control 28 into contacting tower 21 at an intermediate point therein. Pressure control 26 is arranged so that it is responsive to the pressure within tower 21 and is designed to cause little or no pressure drop when the system is operating in a stable fashion, but prevents sudden fluctuations in towerpressure if the rate of production varies. The liquid material from separator 11 in line 24 can also be introduced into tower 21 by opening valve 28 and this is the preferred method of operation since this liquid contains a large proportion of hydrocarbons lighter than butane. As shown, tower 21 consists of two sections both of which are equipped with bubble plate trays or similar devices for insurin intimate contact between gas and liquid phases. The upper section 29 is the contacting section through which the well fluid flows upward and is countercurrently contacted with a cool liquid medium which is less volatile than the distillate to be recovered and miscible therewith supplied through line 39 under control of valve 3|. As stated above the liquid medium is introduced into the upper portion of contacting section 29 in an amount suflicient to raise the critical temperature of the entire composition in section 29 above the temperature existing therein. The well fluid in flowing up contacting section 29 gradually loses its content of distillate hydrocarbons and the residual gas is withdrawn through line 32, recompressed by compressor 33 to a pressure sufflcient to allow its iniection into the producing formation and thence through line 34 and valve 35 to input well 36. Line 32 is equipped with a pressure control device 31 so that the pressure within tower 21 is maintained at a desired value in excess of 1500 pounds per square inch and preferably in the range from about 2000 pounds per square inch to about 4000 pounds per square inch.

Lower section 38 of tower 21 is a stripping section through which the liquid from the bottom of contacting section 29 descends. Heat is supplied to the lower portion of stripping section 38 b means of reboiler 39 thus producing a gas phase which flows upward through stripping section 38 in contact with the descending liquid, the fixed gases continuing to ascend through contacting section 29. By this arrangement the liquid in the bottom of tower 21, which is a mixture of the relatively heavy medium supplied through line 30 and the desired distillate hydrocarbons is kept relatively free from fixed gases such as methane and ethane which would otherwise have to be withdrawn from the system at a lower pressure. The gases stripped from the liquid in stripping section 38 may amount in some cases to as much as of the total residual gas so that it is apparent that compression costs of substantial magnitude are eliminated by operation according to the procedure above described as compared with releasing an equivalent amount of undesirable light gas at a lower pressure.

The composite liquid in the lower portion of tower 21 is removed therefrom under control of liquid level control 40 through line 4| and cooler 42 to the lower portion of flash tower 43. Tower 43 is maintained at a substantially lower pressure than tower 21 and this pressure can suitably lie in the range from about 700 to about 1200 pounds per square inch. Due to the reduction in pressure in tower 43 additional quantities of light hydrocarbons are vaporized and these pass upwardly and are contacted with a descending stream of relatively heavy liquid supplied to the upper portion thereof through line 44 and valve 45. The liquid thus supplied can suitably be of the same type supplied to tower 21 and its purpose is to prevent undue loss of valuable butanes and heavier hydrocarbons. The remaining vapors are withdrawn from the top of tower 43 through line 48, pressure control 41 and line 48 and are compressed by compressor 49 for introduction into line 32 and ultimate reiniection into input well 38. Obviously, of course, this stream can be withdrawn from the system for use as fuel or otherwise, or after compression can be reintroduced into tower 21.

The liquid collecting in the bottom of tower 43 flows through liquid level controlled valve 50 and line 5| into stabilizer 52 which is maintained at a still lower pressure, for example 200 to 400 pounds per square inch. Stabilizer 52 can be of conventional design and as shown has a heating coil 53 in the lower portion thereof to supply the necessary heat and a cooling coil 54 in the upper portion thereof to supply the reflux necessary for eflicient stabilization. The overhead is withdrawn through line 55 and pressure control 56 for use as fuel or other desired purpose, while the stabilized liquid passes through liquid level controlled valve 51 and line 58 into fractionator 59, which is operated at a pressure which may range from about atmospheric to about 50 pounds per square inch.

Fractionator 59 can also be of conventional design and as shown heat is supplied to the lower portion thereof by means of coil 60 and the overhead passes through line GI and condenser 62 to drum 63 in which the desired liquid product is separated from uncondensed gas. This gas is removed from the system through line 84 while the product flows through line 65 to storage. A portion of the product in line 65 is introduced into the upper portion of fractionator 59 as reflux by means of pump 69 and line 81. Obviously fractionator 59 can be operated to produce an overhead product having any desired end point. for example gasoline of an end point of 375 to 400 F. or natural gasoline havin an end point below 300 F. can be obtained.

All of the material not taken overhead is withdrawn from the bottom of fractionator 59 through level controlled valve 68 and line 69 and this will include substantially all of the liquid introduced into towers 21 and 43 through lines 30 and 44 respectively together with that portion of the distillate which boils above the boiling range of the desired product. In my preferred method of operation most of this relatively heavy liquid in line 69 passes through valve 19, line 1|, cooler 12, line 13 and pumps 14 and 15 into lines 30 and 44 for introduction into towers 21 and 43 respectively, while the excess is withdrawn from the system through valve 18 as a heavy product. In starting and one skilled in the art would have no dimculty in arranging apparatus of somewhat different types in order to accomplish equivalent results, for example instead of introducing the extremely volatile liquid in line 24 into tower 21 it can be passed to tower 43 by closing valve 28 and opening valve 19 in line 80. Certain other modifications are illustrated in Figure 2 to which reference is now made. I

In many respects the distillate recovery plant illustrated in Figure 2 is the same as that shown in Figure l and the operation of the various parts thereof is similar except as otherwise hereinafter stated. Distillate-containing ,well fluid from producing well 90 which has been cooled if desired in cooler 9| is introduced intoseparator 92 in which the liquid water and liquid hydrocarbons separate from the gaseous material. Water is withdrawn from the system through line 93 while the liquid hydrocarbons and gaseous hydrocarbons are both introduced into contact tower 94 by means of lines 95 and 96 respectively. Tower 94 differs from tower 21 of Figure l in that it contains a single section of bubble trays or the like and the fluid streams from separator 92 are introduced into the lower portion thereof. tively heavy liquid material is supplied to the upper portion of tower 94 through valve 91 and line 98 so that the gaseous portion of the well fluid is counter-currently contacted therewith. The residual gas flows through line 99, pressure control I00. line IOI, compressor I02, line I03 and valve I04 to input well I05, while the liquid collecting in the bottom of tower 94 flows through line I06 to partial stripper I01. The upper por- 1 tion of stripper I01 is directly connected by line I08 with the lower portion of tower 94 above the liquid level so that tower 94 and stripper I01 are at substantially the same pressure. Heating coil I09 in the lower portion of stripper I01 supplies the heat necessary to vaporize a substantial portion of the methane and ethane in the liquid supplied thereto and this gaseous fraction passes through line I08 to be contacted with the heavy liquid from line 98 to prevent excessive loss of butanes and heavier hydrocarbons.

The partially stripped liquid flows through liquid level controlled valve H0, cooler III and valve II2 to separator II3 which is maintained at a substantially lower pressure, for example 700 to 1200 pounds per square inch. The vapors evolved at this pressure pass upward in contact with reflux due to cooling coil H4 in the upper portion of separator H3 and the fixed gases are withdrawn through line H5, pressure control H6,

compressor I I1 and line I I8 to line I08 for further treatment in tower 94 arid ultimate reinjection through input well I05. The remaining liquid collecting in the bottom of separator H3 passes through liquid level controlled valve I I9 and line I thence through valve I2I to the top portion of fractionator I22 which is maintained at a relatively low pressure, for example about 50 pounds per square inch.

As an alternate procedure, the liquid in line I20 may be caused to pass through valve I23 into fractionator I22 at a point a few plates below the top plate, so that the reflux from the top plates will keep down the end-point of the finished gasoline from stabilizer I31.

Sufilcient heat is supplied to the lower portion of fractionator I22 by means of heating coil I24 so that all of the desired distillate hydrocarbons are driven overhead through line I25 while the fraction heavier than the desired product flows Relatower 94.

from the bottom thereof through level controlled valve I26, line I21 and either through valve I28 to storage or preferably for the most part through valve I29, line I30, cooler I3I, line I32 and pump I33 to line 98 for reintroduction into contact As in Figure 1 an extraneous heavy oil can be introduced into the system by means of line I34 and valve I35.

The vapors in line I25 still contain a considerable quantity of hydrocarbons too light for'use in either motor gasoline or natural gasoline and consequently they are passed by means of pump I36 directly into stabilizer I31 which operates in the usual manner, preferably at a pressure in the range from 200 to 400 pounds per square inch. Gasoline having the desired characteristics is taken off as bottoms through line I38 and cooler I39 while the overhead passes through pressure control valve I40 and cooler I4I to stabilizer reflux drum I42. Fixed gas passes from the system through line I43 while the volatile liquid in drum I42 is withdrawn through line I44 and a. portion thereof is introduced into the top of stabilizer I31 as reflux through pump I45 and valve I46.

Many details which have been omitted in the above description have not been given in order that ,my invention can be more readily understood, such details, however, being easily supplied by those skilled in the art. Among them are the construction and operation of the apparatus according to my invention for any particular well fluid or fluids, the use of indirect heat exchange at various points in order to conserve heat, etc. Furthermore, it is obvious that the fluid from a plurality of distillate wells can be combined 7 and the distillate recovered therefrom according to my invention in the same manner as hereinabove described for the fluid from a single well, and that a plurality of input wells can likewise be used.

While I have described my invention in connection with certain specific embodiments thereof, it is to be understood that these are by way of illustration and not by way of limitation, and that I do not mean to be bound thereby but only by the appended claims in which I have defined my invention.

I claim:

1. A method of recovering gasoline-range distillate hydrocarbons from a high pressure well fluid containing the same which comprises contacting said well fluid in a contacting zone with a liquid absorption medium having an initial boiling point of at least 260 F., said boiling point being sufliciently high to permit the recovery of said distillate hydrocarbons from said liquid ah sorption medium by distillation therefrom, said contacting being conducted at a pressure in excess of about 1500 pounds per square inch, separately removing residual gas and a liquid fraction including said liquid absorption medium and said distillate hydrocarbons from said contacting zone, introducing said liquid fraction into a separation zone maintained at a pressure within the range from about 700 to about 1200 pounds per square inch, removing the gases evolved in said separation zone from the upper portion thereof, removing a liquid fraction from the lower portion of said separation zone, and recovering said distillate hydrocarbons from said last mentioned liquid fraction by distillation therefrom.

2. The method of recovering distillate hydrocarbons from a high pressure well fluid containing the same which comprises contacting said well fluid in a contacting zone with a liquid medium substantially less volatile than, and miscible with, the distillate to be recovered, at a pressure in excess of about 1500 pounds per square inch,

' separately removing residual gas and a liquid fraction including said liquid medium and said distillate hydrocarbons from said contacting zone, heating said liquid fraction under a pressure substantially the same as that in said contacting zone to produce a vapor fraction containing light gaseous hydrocarbons and a second liquid fraction therefrom, returning said vapor fraction to said contacting zone, introducing said second liquid fraction into a separation zone maintained at a pressure in the range from about 700 to about 1200 pounds per square inch, removing the gases evolved in said separation zone from the upper portion thereof, removing a third liquid fraction from the lower portion of said separation zone, and recovering distillate hydrocarbons from said third liquid fraction.

3. The method of claim 2 including the step of introducing another portion of said liquid medium into the upper portion of said separation zone to contact said gases evolved therein.

4. The method of claim 2 including the steps of compressing said gases from said separation zone and introducing said compressed gases into said contacting zone.

5. The method of recovering distillate hydrou carbons froma high pressure well fluid containing the same which comprises contacting said well fluid in a contacting zone with a liquid absorption medium substantially less volatile than and miscible with said distillate hydrocarbons, said liquid absorption medium having an initial boiling point sufliciently high to permit recovery of said distillate hydrocarbons from said liquid absorption medium by distillation, said contacting being conducted at a pressure in excess of about 1500 pounds per square inch, separately removing residual gas and a liquid fraction including said liquid absorption medium and said distillate hydrocarbons from said contacting zone, cooling said liquid fraction to a temperature lower than the temperature existing in said contacting zone, introducing said cooled liquid fraction into a separation zone maintained at a superatmospheric pressure substantially lower than the pressure of said contacting step, contacting gases evolved in said separation zone with another portion of liquid absorption medium and recovering distillate hydrocarbons from said last mentioned portion of said liquid absorption medium after contacting said gases and from the liquids remaining after the evolution of said last mentioned gases, and recycling said liquid absorption medium, from which said distillate hydrocarbons have been recovered, to said contacting zone and to said last mentioned contacting step.

6. The method of recovering distillate hydrocarbons from a high pressure well fluid containing the same which comprises contacting said well fluid in a contacting zone with a liquid absorption medium substantially less volatile than and miscible with said distillate'hydrocarbons, said liquid absorption. medium having an initial boiling point sufficiently high to permit recovery of said distillate hydrocarbons from said liquid absorption medium by distillation, said contacting being conducted at a pressure in excess of about 1500 pounds per square inch, separately removing residual gas and a liquid fraction including said liquid absorption medium and said distillate hydrocarbons from said contacting zone, cooling said liquid fraction to a temperature lower than the temperature existing in said contacting zone, introducing said cooled liquid fraction into a separation zone maintained at a pressure within the range from about 700 to about 1200 pounds. per square inch, contacting gases evolved in said separation zone with another portion of liquid absorption medium and recovering distillate hydrocarbons from said last mentioned portion of said liquid absorption medium after contacting said gases and from the liquids remaining after the evolution of said last mentioned gases, and recycling said liquid absorption medium, from which said distillate hydrocarbons have been recovered, to said contacting zone and to said last mentioned contacting step.

'7. The method of recovering distillate hydrocarbons from a high pressure well fluid containing the same which comprises contacting said well fluid in a contacting zone with a liquid absorption medium substantially less volatile than and miscible with the distillate hydrocarbons to be recovered, said liquid absorption medium having an initial boiling point sufiiciently high to permit recovery of said distillate hydrocarbons from said liquid absorption medium by distillation, said contacting being conducted at a pressure in excess of about 1500 pounds per square inch, separately removing residual gas and a liquid fraction including said liquid absorption medium and said distillate hydrocarbons from said contacting zone, introducing said liquid fraction into a zone the upper portion of which constitity of said liquid absorption medium in said second contacting zone, removing residual gases from the upper portion of said second contacting zone, removing liquid hydrocarbons containing said liquid absorption medium and said distillate hydrocarbons from the lower portion of said separation zone, distilling said liquid hydrocarbons to separate said distillate hydrocarbons from said liquid absorption medium, and recycling at least a substantial part of said liquid absorption medium to said first mentioned contacting zone and to said second' contacting zone.

EARLS.I-IIIL. 

